Rheem RGDG, Installation Instructions Manual, Page: 11 / 48

Combustion air must be free of acid
forming chemicals; such as sulphur,
fluorine and chlorine. These elements
are found in aerosol sprays,
detergents, bleaches, cleaning
solvents, air fresheners, paint and
varnish removers, refrigerants and
many other commercial and household
products. Vapors from these products
when burned in a gas flame form acid
compounds. The acid compounds
increase the dew point temperature of
the flue products and are highly
corrosive after they condense.
ALL FURNACE INSTALLATIONS
MUST COMPLY WITH THE
NATIONAL FUEL GAS CODE AND
LOCAL CODES TO PROVIDE
ADEQUATE COMBUSTION AND
VENTILATION AIR FOR THE
FURNACE. FAILURE TO DO SO CAN
CREATE HAZARDOUS CONDITIONS
RESULTING IN PROPERTY
DAMAGE, BODILY INJURY OR
DEATH FROM SMOKE, FIRE OR
CARBON MONOXIDE.
Combustion air requirements are
determined by whether the furnace is
in an open (unconfined) area or in a
confined space such as a closet or
small room.
EXAMPLE 1.
FURNACE LOCATED IN AN
UNCONFINED SPACE
Using indoor air for combustion.
An unconfined space must have at
least 50 cubic feet for each 1,000 Btuh
of the total input for all appliances in
the space. Here are a few examples of
the room sizes required for different
inputs. The sizes are based on 8 foot
ceilings.
Btuh Minimum Sq. Feet Typical Room Size
Input With 8' Ceiling With 8' Ceiling
45,000 281 12
*
x24
*
or 16
*
x18
*
50,000 312 14
*
x24
*
or 18
*
x18
*
67,500 421 15
*
x28
*
or 20
*
x21
*
75,000 469 15
*
x31
*
or 20
*
x24
*
100,000 625 20
*
x31
*
or 25
*
x25
*
125,000 833 23
*
x34
*
or 26
*
x30
*
150,000 938 25
*
x38
*
or 30
*
x31
*
If the open space containing the
furnace is in a building with tight
construction (contemporary
construction), outside air may still be
required for the furnace to operate and
vent properly. Outside air openings
should be sized the same as for a
confined space.
11
WARNING
!
FIGURE 8
AIR FROM ATTIC/CRAWL SPACE
EXAMPLE 2.
FURNACE LOCATED IN A
CONFINED SPACE
A confined space (any space smaller
than shown above as “unconfined”)
must have openings into the space
which are located in accordance with
the requirements set forth in the
following subsections A and B. Size the
openings by how they are connected to
the heated area or to the outside, and
by the input of all appliances in the
space.
If confined space is within a building
with tight construction, combustion air
must be taken from outdoors or area
freely communicating with the
outdoors.
A. USING INDOOR AIR FOR
COMBUSTION
IMPORTANT: Air should not be taken
from a heated space with a fireplace,
exhaust fan or other device that may
produce a negative pressure.
If combustion air is taken from the
heated area, the openings must
each have at least 100 square
inches of free area. Each opening
must have at least one square inch
of free area for each 1,000 Btuh of
total input in the space. Here are
some examples of typical openings
required.
Btuh Free Area
Input Each Opening
45,000 100 Square Inches
100,000 100 Square Inches
150,000 150 Square Inches
B. USING OUTDOOR AIR FOR
COMBUSTION
IMPORTANT: NEVER TAKE
COMBUSTION AIR FROM AN
ATTIC SPACE THAT IS
EQUIPPED WITH POWER
VENTILATION.
The confined space must
communicate with the outdoors
according to Methods 1 and 2. The
minimum air opening dimension
shall not be less than 3 inches.
When using ducts, they shall be of
the same cross-sectional area as
the free area of the openings to
which they connect.
Method 1
Provide two permanent openings,
one located within 12 inches of the
top and one located within 12 inches
of the bottom of the enclosure. Each
opening shall communicate directly,
or by ducts, with the outdoors or
spaces (crawl or attic) that freely
communicate with the outdoors.
a. Where directly communicating
with the outdoors or where
communicating to the outdoors
through
VERTICAL DUCTS, each
opening shall have a minimum
free area of
1 square inch for
each 4000 BTUH
of total
appliance input rating in the
enclosure. Here are typical duct
sizes.